Enzymatic synthesis of a 6'-sulphated sialyl-lewis which is an inhibitor of L-selectin binding to peripheral addressin

A sulphated form of sialyl-Lewis^x, NeuAcα2-3Galβ1-4(Fucα1-3)GlcNAc6OSO₃β1-3Gal, was synthesized enzymatically from a precursor disaccharide, GlcNAc6OSO₃β1-3Gal, using sequential steps involving β1,4-galactosyltransferase, α2,3-trans-sialidase and recombinant α1,3-fucosyltransferase, respectively. Successful enzymatic fucosylation at the 3 position of the GlcNAc6OSO₃ residue demonstrated that fucosyltransferases are capable of generating, in situ, sulphated sialyl Lewis^x structures containing sulphate at the 6 position of GlcNAc. The sulphated sialyl-Lewis^x pentasaccharide produced by this procedure inhibited binding of a soluble form of L-selectin to ³⁵SO₄-labelled peripheral addressin with an IC₅₀ of 0.8 mM, whereas sialyl-Lewis^x tetrasaccharide was a weaker inhibitor, displaying an IC₅₀ of 3.2 mM. Hemmerich and Rosen (Biochemistry, 33, 4820-4829, 1994) recently reported the presence of Galβ1-4GlcNAcO6SO₃ structures on murine peripheral addressin Sgp50, in addition to sialyl Lewis^x structures sulphated at the 6-O-galactose position. Based on our data, we suggest that sialyl Lewis^x sulphated at the 6-O-GlcNAc position may also exist on receptors and function as a ligand for L-selectin.